How not to make a mess of a crown moulding job

O foul is me
In math as ever,
Behold the mess
I am not clever.

I strove to make
A lovely moulding,
My heart doth ache
On the beholding.

If ever you need an excuse to swear, install crown moulding in your home. In any room. No matter how small. It will unleash your inner hellbeast, and utterly degrade your inner mathematician.

If one of your New Year's resolutions involves limiting your potty mouth, don't attempt this project.

Also, don't attempt this project without a compound mitre saw that says right on the package "Makes crown moulding easy!" And the box should also have a guarantee that if your crown moulding tanks owing to pilot error, you get double your money back. And free psychological counselling.

Crown This

Crown moulding is available in various composites (basically cardboard or plastic) or in real wood, usually clear pine. Prime and paint the stuff before installing it. It's way easier than standing on a ladder with a neck ache trying not to slime the ceiling or walls with errant trim paint. TIP: Prime pine moulding with a stain-blocking primer so that knots or pitch pockets won't bleed sappily through the paint.

You can buy moulding that has pre-made corners, but it never quite makes it into the Worldwide Compendium of Good-looking Carpentry. It has an appearance that screams, "Oh gosh, what did humans ever do before the invention of labour-saving home decorating materials?" and answers itself, "We had actual skill."

Math Market

Buy MORE than you need. If you got 11% in Grade 10 math like I did, buy WAY more than you need, because getting the compound angle corners just right is more difficult than childbirth.

Choose the moulding to match the proportions of the room. If you have high ceilings you can select fairly broad, and possibly ornate, moulding. If you have 7-1/2 foot ceilings, wide moulding will feel more oppressive than a long car trip with a bossy relative. And I would know.

Buy some short samples and tack them in place to make sure the moulding style feels good in the room. I'll tell you what helps it feel good - a few martinis. Why do math sober when the odds are just as good that you'll screw up?

Ample Sample

The first thing to do is to make sample corners for each of the corners in the room. Most rooms will just have inside corners, unless there are jogs and alcoves. Because walls and ceilings are never usually square or plumb or level or flat, you will find subtle angle differences (which, by the way, the pre-fabricated corners will NEVER accommodate) are necessary to create a tight-fitting joint. Or even a vaguely fitting joint.

Most compound mitre saw manuals describe how to cut crown moulding. But they usually assume you're making 45-degree angles for a perfectly square room. Start with 12-inch sample pieces cut at precisely 45 degrees, and see whether you need to add a little to the point, or take a little off. Mark the samples, go back to the saw, cut the fresh angle, and go back to the room with the sample pieces. Repeat until you get it right. By the time the angle is correct, you will probably be holding 3-inch pieces. Copy these cuts on the full-length boards. Label each board as you go ("south wall") so you don't get mixed up during installation.

When you start installing the moulding, you will likely find that the ceiling is not flat, and there are wows and waves in it. Tack each piece of moulding in the center so it's held in place. Then work on the corners first. Put a little carpenter's glue on the corner joints and make them meet precisely. Use shims to force the boards into position so the corners look really tight, then nail them in place. The corner thing can be a frustrating exercise (huge understatement). Send small children out of the room.

The next goal is to fasten the rest of the board, driving a finish nail wherever the board is tight to the wall or ceiling (roughly every 12" - 18"). Leave the nail heads protruding about a quarter-inch so you don't put hammer tracks all over your nice new moulding.

When you're done nailing all the moulding in position, caulk the top and bottom borders of the crown moulding to remove shadows and gaps caused by wavy walls and ceilings. TIP: Don't caulk the corners - the caulk just gets messy. Instead, fill the corner joints with lightweight spackling compound and retouch with matching paint.

CAULK TIP: Use DAP's Painter's Acrylic Latex Caulk - don't use caulk with silicone!
NAIL TIP: Rent or borrow an air compressor and finish nail gun and the whole job will be eminently faster with a lot less swearing, sweating and hypertension.

Drive the finish nails deep into the boards with a nail set, then fill the holes with lightweight spackling compound, and retouch the paint. You'll also probably have to retouch the walls and ceiling everywhere you've pounded your fist through the drywall.